Honor 80 character limit in 'zpool status'

This is a minor nit, but the second line of the 'action' message
when you need to upgrade your pool to support feature flags exceeds
the standard 80 character limit.  Fix it by moving the word
'feature' on to the third line.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>